Bone Density Scan (cont.)

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What is bone mineral density (BMD)?

The absolute amount of bone as measured by bone mineral density (BMD) testing generally correlates with bone strength and its ability to bear weight. The BMD is measured with a dual energy X-ray absorptiometry test (referred to as a DXA scan). By measuring BMD, it is possible to predict fracture risk in the same manner that measuring blood pressure can help predict the risk of stroke.

It is important to remember that BMD testing cannot predict the certainty of developing a fracture. It can only predict risk. It is also important to note that a bone density scan, or test, should not be confused with a bone scan, which is a nuclear medicine test in which a radioactive tracer is injected that is used to detect tumors, cancer, fractures, and infections in the bone.

The World Health Organization has developed definitions for low bone mass (osteopenia) and osteoporosis. These definitions are based on a T-score. The T-score is a measure of how dense a patient's bone is compared to a normal, healthy 30-year-old adult.

Normal: A bone BMD is considered normal if the T-score is within 1 standard deviation of the normal young adult value. Thus a T-score between 0 and -1 is considered a normal result. A T-score below -1 is considered an abnormal result.

Low bone mass (medically termed osteopenia): A BMD defines osteopenia as a T-score between -1 and -2.5. This signifies an increased fracture risk but does not meet the criteria for osteoporosis.

Osteoporosis: A BMD greater than 2.5 standard deviations from the normal (T score less than or equal to -2.5) defines osteoporosis.

Based on the above criteria, it is estimated that 40% of all postmenopausal Caucasian women have osteopenia and that an additional 7% have osteoporosis.

Medically Reviewed by a Doctor on 9/24/2013

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